The principal objective of the research is to correlate reported changes in the potassium flux produced by ultrasound with changes in cell growth. We shall use a mouse neuroblastoma cell line for which a relationship between K ion flux and cell growth under normal culture conditions has already been established. If the correlation is found, as expected, a secondary objective is to investigate differences reported in other studies, to determine the influence of extracellular environmental conditions -- e.g., the presence or absence of various ions and buffers -- during insonation. Radioactive tracer techniques will be used to determine ion fluxes, and thymidine incorporation and time-lapse cinematography will be used to monitor cell growth. A well-calibrated ultrasound exposure facility is available. We shall seek a coherent explanation of the effects of ultrasound on cell growth through its influence on ion transport as a potentially common mechanism. Because nerve cells are among the most sensitive in the human body and, when differentiated, do not divide, the neuroblastoma cell line is also highly suited to establishing the thresholds of the ultrasonic bioeffects to be investigated in this research. Knowledge of thresholds is required for establishing reasonable safety standards for the use of ultrasound in diagnosis and therapy -- e.g., in monitoring fetal development, or stimulating tissue regeneration in healing wounds.